SRWE MODULE 14: ROUTING CONCEPTS | COMPLETE PRACTICE QUESTIONS,
ANSWERS & STUDY GUIDE 2026/2027
What are the 2 functions of a router? - ANS ✔✔- determine the best path to forward packets based on
the information in its routing table
- forward packets to their destination
+ encapsulate packets in the appropriate data link frame type for the outgoing interface
+ ex. Serial link could be PPP (Point-to-Point Protocol), HDLC (High-Level Data Link Control), or another
Layer 2 protocol), instead of Ethernet
Describe routing. - ANS ✔✔- the function a router makes to determine which interface to use to forward
the packet to the destination, after receiving an IP packet on an interface
What is required for there to be a match between the destination IP address of a packet and a route in
the routing table?
What determines this? - ANS ✔✔- a minimum number of far-left bits must match between the IP
address of the packet and the route in the routing table
+ the route with the greatest number of matching bits in the far left is the preferred route
- the prefix length of the route in the routing table
Describe directly connected networks. - ANS ✔✔- networks configured on the active interfaces of a
router
+ added to the routing table when an interface is configured with an IP address and subnet mask (prefix
length) and is active (up and up)
Describe remote networks, from the perspective of the router. - ANS ✔✔- networks not directly
connected to the router, learned about in 2 ways
- Static routes
+ manually added to routing table
- Dynamic routing protocols
+ dynamically learned about through Dynamic routing protocols (EIGRP- Enhanced Interior Gateway
Routing Protocol, OSPF- Open Shortest Path First. etc.)
Describe a default route.
Why do most enterprise networks use a default route in their routing table? - ANS ✔✔- No bits must be
matched between the default route and the destination IP address
+ 0.0.0.0/0 IPv4 route entry
+ ::/0 IPv6 route entry
- aka Gateway of Last Resort
- next hop router to use when the routing table does not contain a specific route that matches the
destination IP address
, - either static or dynamically learned from a dynamic routing protocol
- to reduce the number of routes in a routing table, as multiple network may use the same first hop out
anyway
Describe the 3 options a router does after determining the best path for a packet that it has received.
Include the specific follow-on actions that the router must take based on the packet being either IPv4 or
IPv6. - ANS ✔✔- Directly connect network path
+ Forwards packet to the indicated directly-connected device using MAC address listed for that IP
address in its ARP table (if IPv4) or Neighbor Cache (if IPv6)
+ if not in ARP Table or Neighbor cache, router gets the MAC address by ARP request (if IPv4) or
Neighbor Solicitation (if IPv6)
- Remote network
+ forwards to next-hop router, as indicated in the route entry
+ if next hop router is on an Ethernet network, ARP or ICMPv6 Neighbor Discovery will determine MAC
address of the next-hop router
- No match (nor default route)
+ drops packet
Since there is no MAC addresses on serial interfaces, what does a router set the data link destination to,
when it it sends a frame out of a serial interface? - ANS ✔✔- the equivalent of a broadcast
What is the purpose of packet forwarding mechanisms?
Describe each of the 3 packet forwarding mechanisms. - ANS ✔✔- to more efficiently encapsulate
packets in the appropriate data link frame type for the outgoing interface IOT speed up the the time it
take a router to forward packets
- Process Switching
+ older, very-slow, and rarely implemented Cisco mechanism
+ each packet match by router CPU to an entry in the routing table
+ Process switching solves a problem by doing math long hand, even if it is the identical problem that
was just solved.
- Fast Switching
+ older Cisco mechanism, successor to process-switching
+ only one packet in a flow is process switched; remaining packets with same destination IP uses info in a
Fast-switching cache for its switching
+ router Fast Switching (fast-forward) Cache stores next-hop information
+ Analogy: Fast switching solves a problem by doing math long hand one time and remembering the
answer for subsequent identical problems.
- Cisco Express Forwarding (CEF)
+ most recent and default Cisco IOS packet-forwarding mechanism
+ network converges and router builds FIB (Forward Information Base/Adjacent Table that has all
information that a router needs to forward a packet
ANSWERS & STUDY GUIDE 2026/2027
What are the 2 functions of a router? - ANS ✔✔- determine the best path to forward packets based on
the information in its routing table
- forward packets to their destination
+ encapsulate packets in the appropriate data link frame type for the outgoing interface
+ ex. Serial link could be PPP (Point-to-Point Protocol), HDLC (High-Level Data Link Control), or another
Layer 2 protocol), instead of Ethernet
Describe routing. - ANS ✔✔- the function a router makes to determine which interface to use to forward
the packet to the destination, after receiving an IP packet on an interface
What is required for there to be a match between the destination IP address of a packet and a route in
the routing table?
What determines this? - ANS ✔✔- a minimum number of far-left bits must match between the IP
address of the packet and the route in the routing table
+ the route with the greatest number of matching bits in the far left is the preferred route
- the prefix length of the route in the routing table
Describe directly connected networks. - ANS ✔✔- networks configured on the active interfaces of a
router
+ added to the routing table when an interface is configured with an IP address and subnet mask (prefix
length) and is active (up and up)
Describe remote networks, from the perspective of the router. - ANS ✔✔- networks not directly
connected to the router, learned about in 2 ways
- Static routes
+ manually added to routing table
- Dynamic routing protocols
+ dynamically learned about through Dynamic routing protocols (EIGRP- Enhanced Interior Gateway
Routing Protocol, OSPF- Open Shortest Path First. etc.)
Describe a default route.
Why do most enterprise networks use a default route in their routing table? - ANS ✔✔- No bits must be
matched between the default route and the destination IP address
+ 0.0.0.0/0 IPv4 route entry
+ ::/0 IPv6 route entry
- aka Gateway of Last Resort
- next hop router to use when the routing table does not contain a specific route that matches the
destination IP address
, - either static or dynamically learned from a dynamic routing protocol
- to reduce the number of routes in a routing table, as multiple network may use the same first hop out
anyway
Describe the 3 options a router does after determining the best path for a packet that it has received.
Include the specific follow-on actions that the router must take based on the packet being either IPv4 or
IPv6. - ANS ✔✔- Directly connect network path
+ Forwards packet to the indicated directly-connected device using MAC address listed for that IP
address in its ARP table (if IPv4) or Neighbor Cache (if IPv6)
+ if not in ARP Table or Neighbor cache, router gets the MAC address by ARP request (if IPv4) or
Neighbor Solicitation (if IPv6)
- Remote network
+ forwards to next-hop router, as indicated in the route entry
+ if next hop router is on an Ethernet network, ARP or ICMPv6 Neighbor Discovery will determine MAC
address of the next-hop router
- No match (nor default route)
+ drops packet
Since there is no MAC addresses on serial interfaces, what does a router set the data link destination to,
when it it sends a frame out of a serial interface? - ANS ✔✔- the equivalent of a broadcast
What is the purpose of packet forwarding mechanisms?
Describe each of the 3 packet forwarding mechanisms. - ANS ✔✔- to more efficiently encapsulate
packets in the appropriate data link frame type for the outgoing interface IOT speed up the the time it
take a router to forward packets
- Process Switching
+ older, very-slow, and rarely implemented Cisco mechanism
+ each packet match by router CPU to an entry in the routing table
+ Process switching solves a problem by doing math long hand, even if it is the identical problem that
was just solved.
- Fast Switching
+ older Cisco mechanism, successor to process-switching
+ only one packet in a flow is process switched; remaining packets with same destination IP uses info in a
Fast-switching cache for its switching
+ router Fast Switching (fast-forward) Cache stores next-hop information
+ Analogy: Fast switching solves a problem by doing math long hand one time and remembering the
answer for subsequent identical problems.
- Cisco Express Forwarding (CEF)
+ most recent and default Cisco IOS packet-forwarding mechanism
+ network converges and router builds FIB (Forward Information Base/Adjacent Table that has all
information that a router needs to forward a packet
